Dormant Ear Spring, located on Yellowstone National Park’s Geyser Hill, spewed steam on Sept. 15 in its biggest blow since 1957, park spokesman Neal Herbert told The Associated Press. And among the more intriguing artifacts it belched out is a baby’s pacifier that could date back as far as the 1930s.

More mundane objects collected by park staffers included a large cement block, rusted metal cans, dozens of coins, a bear-designed cloth that could be part of either a shirt or a bag and a black metal, plastic container.

“Foreign objects can damage hot springs and geysers. The next time Ear Springs erupts we hope it’s nothing but natural rocks and water,” a rep posted on the official Facebook park page. “You can help by never throwing anything into Yellowstone’s thermal features!”

The items are expected to be inventoried by curators and could possibly end up in Yellowstone’s archives.

Geyser Hill has been experiencing more eruptive activity in recent weeks, which includes new surface fractures and vents. A boardwalk that leads tourists to the Upper Geyser Basin has been cordoned off due to the threat of boiling-hot water. The liquid from Ear Spring traveled between 20 and 30 feet high.

“Shifts in hydrothermal systems occur only in the upper few hundred feet of the Earth’s crust and are not directly related to movement of magma several kilometers deep,” noted the U.S. Geological Survey. “There are no signs of impending volcanic activity.”